The present invention is directed to a strapping machine. More particularly, the present invention is directed to an improved tension control system for tensioning a strap around a load in a strapping machine.
Strapping machines are in widespread use for securing straps around loads. There are various types of strappers. One type of strapper is a stationary arrangement in which the strapper is stand-alone device that is part of an overall manufacturing of fabrication operation.
In a stand-alone strapper, a strapping head and drive mechanisms (feed and take-up) are typically mounted within a frame. A chute is likewise mounted to the frame, through which the strapping material is fed.
In one known configuration, a strapping head is mounted at about a work surface, and the chute is positioned above the work surface and above the strapping head. Strap material is fed to the strapping head, and is then driven by feed wheels (by a motor) to feed the strap materials through the strapping head and around the chute back to the strapping head. Once the strap material is fed back to the strapping head, a gripping arrangement grips the strap material and the same motor used to feed the strap material around the chute is reversed and the strap material is stripped from the chute and tensioned around the load. The tensioned strap is then gripped by a second part of the gripping arrangement and the motor is turned off. A cutter in the strapping head cuts the tensioned strap (from the source or supply) and the strapping head forms a seal in the strapping material, sealing the strapping material to itself around the bundled load.
Proper strap tension is achieved by various means. Tension can be controlled mechanically by the use of a mechanical clutch. Alternatively, tension can be controlled by varying the voltage to a drive clutch associated with the motor. When the tension applied to the strap overcomes the voltage being sent to the drive clutch, the clutch slips and continues to slip for a predetermined period of time. Once that time expires, tension is considered complete, whereupon the strap material is cut and the motor and clutch are turned off. However this can result in wear on the clutch, and variability in the tension applied to the strap material
Accordingly, there exists a need for a more effective and consistent method for tensioning strapping material around a load in a stationary strapper.